1. Field of the Invention
The present invention relates to a rectangular parallelepipedic case and a method of producing the same. More particularly, the present invention relates to a rectangular parallelepipedic case or quadrangular prismatic case, in which unwanted deformation is easily avoided, and which has high rigidity and durability, and a method of producing the same.
2. Description Related to the Prior Art
JP-Y (Japanese Utility Model Publication No.) 49-44073 discloses a method of producing a rectangular parallelepipedic case or quadrangular prismatic case by bending a plate of thermoplastic synthetic resin. JP-B (Japanese Patent Publication No.) 48-860 discloses a method of producing a hollow plastic plate. Synthetic resin is formed by a technique of extrusion into the hollow plastic plate in which there are partition portions that are extended in a single direction of the extrusion, and inside the hollow plastic plate, a great number of long and thin hollow chambers are defined between adjacent two of the partition portions.
The hollow plastic plate is advantageous over a plate without the hollow chambers, because of its light weight, economy of material for production, and also high rigidity. The hollow plastic plate is widely used for boxes manufactured in mass production, and for containers containing articles with heavy weight. To produce the rectangular parallelepipedic case from a hollow plastic plate, plural bend lines are drawn on the hollow plastic plate at first, and then the plate is bent along the bend lines to build the rectangular parallelepipedic case.
If the rectangular parallelepipedic case or quadrangular prismatic case has a large size, there occurs a problem of deformation despite such an advantageous use of a hollow plastic plate. When lateral walls rising from a bottom wall have a great width, it is likely that centers of the lateral walls protrude outwards and are deformed in an expanded form. A top lid may be associated with the rectangular parallelepipedic case of which a top is open. But the deformation is likely to cause failure in fitting the top lid on the open top of the rectangular parallelepipedic case, because edges of the open top are likely to expand. Furthermore this deformation is visually not agreeable.
To avoid deformation of the case, it is known to secure a reinforcing frame or auxiliary plate on the outside or inside of the lateral walls. However this inevitably increases the total weight of the rectangular parallelepipedic case or quadrangular prismatic case. Problems occur in high cost and relatively small inner volume.
A photographic paper magazine is used for containing photographic paper. The photographic paper magazine has a quadrangular prismatic shape, and contains a core in a rotatable manner. Photographic paper is wound about the core in a roll form. EP-A 0 561 438 (corresponding to JP-A (Japanese Patent Laid-open Publication No.) 6-130569) discloses a photographic paper magazine formed from plastic by a method of extrusion. U.S. Pat. No. 5,232,175 discloses a photographic paper magazine formed from plastic by injection molding.
The plastic magazine is favorable, as it has a high durability. However there is no known plastic magazine more advantageous than a photographic paper magazine produced from cardboards, in view of its weight, portability, and ease of production.